Glenoid component for shoulder arthroplasty

ABSTRACT

A glenoid component apparatus for shoulder arthroplasty includes a bearing portion and a stem portion connected to the bearing portion. The stem portion is modeled from a normalized glenoid vault morphology. A method for making a glenoid component for shoulder arthroplasty includes obtaining a model of a normalized glenoid vault morphology and producing a stem portion of the glenoid component based on the model.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopedics,and, more particularly, to glenoid component apparatuses for shoulderarthroplasty and methods for making them.

BACKGROUND

Arthroplasty is the surgical replacement of one or more bone structuresof a joint with one or more prostheses. Shoulder arthroplasty ofteninvolves replacement of the glenoid fossa of the scapula with aprosthetic glenoid component. The conventional glenoid componenttypically provides a generally laterally or outwardly facing generallyconcave bearing surface against which a prosthetic humeral head (or,alternatively, the spared natural humeral head in the case of a glenoidhemi-arthroplasty) may bear during operation of the joint. Theconventional glenoid component typically also includes a generallymedially or inwardly projecting stem for fixing the glenoid component ina cavity constructed by suitably resecting the glenoid fossa andsuitably resecting cancellous bone from the glenoid vault.

Various stem designs have been proposed for ensuring proper alignmentand secure and lasting fixation of the glenoid component within theglenoid vault. However, the glenoid vault has a complex morphology.While three-dimensionally shaping a stem for compatibility with theendosteal walls of the glenoid vault can potentially significantlyenhance fixation of the glenoid component, historical designs have nottaken full advantage of this opportunity.

One advantageous approach is described in co-pending application Ser.No. 10/259,045, published on Apr. 1, 2004 as US2004/0064189 A1 andentitled “Concave Resurfacing Prosthesis”, the disclosure of which isincorporated herein by reference. In this approach, a glenoid componentis fitted to at least partially fill a cavity formed in the glenoidvault. The component has a generally oval inverted dome shape togenerally conform to the shape of the vault. However, it is recognizedin the '045 Application that exact sizing of the glenoid component tothe vault cavity is made difficult by the unique anatomy of eachpatient. To address this difficulty, the '045 Application disclosesproviding a series of differently sized glenoid components.

There remains a need for a glenoid component that is more nearly sizedand shaped in three-dimensions to fill the cavity in the glenoid vault.There is a further need for a technique that facilitates preparation ofsuch a component, and especially a component that has more universalapplicability to the anatomy of most patients.

SUMMARY OF THE INVENTION

The present invention provides a glenoid component apparatus forshoulder arthroplasty. The apparatus includes a bearing portion andfurther includes a stem portion extending from the bearing portion. Thestem portion models a normalized or pathologic glenoid vault morphology.

In an alternative embodiment, the present invention provides a methodfor making a glenoid component for shoulder arthroplasty. The methodincludes obtaining a model of a normal or pathologic glenoid vaultmorphology and further includes producing a portion of the glenoidcomponent based on the model.

In another alternative embodiment, the present invention provides aglenoid component apparatus for a shoulder joint including at least oneof a natural humeral component and a prosthetic humeral component. Theapparatus includes a means for bearing against at least one of thenatural humeral component and the prosthetic humeral component. Theapparatus further includes a means, extending from the bearing means,for modeling a normal glenoid vault morphology.

The above-noted features and advantages of the present invention, aswell as additional features and advantages, will be readily apparent tothose skilled in the art upon reference to the following detaileddescription and the accompanying drawings, which include a disclosure ofthe best mode of making and using the invention presently contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective view of an exemplary shoulderprosthesis including an exemplary glenoid component according to thepresent invention;

FIG. 2 a, FIG. 2 b, and FIG. 2 c show a flow diagram of an exemplarymethod for configuring the stem of the prosthesis of FIG. 1 to model anormal or pathologic glenoid vault morphology;

FIG. 3 shows a rectangular (“Cartesian”) coordinates reference systemrelative to the plane body of a typical scapula as defined by threesurface points of the scapula;

FIG. 4 shows the superior-inferior (“SI”) dimension and theanterior-posterior (“AP”) dimension of the typical glenoid fossa;

FIG. 5 shows a table listing exemplary range and exemplary average SIdimension for six exemplary sub-groups of scapulae from a scapulaesample based on their SI dimensions;

FIG. 6 shows an exemplary substantially complete tracing (toward theinferior end of the typical glenoid fossa) of the endosteal walls of thetypical glenoid fossa;

FIG. 7 shows an exemplary partial tracing (toward the inferior end ofthe typical glenoid fossa) of the endosteal walls of the typical glenoidfossa as a result of fossa occlusion in the region of the typicalscapular spine;

FIG. 8 shows views of a volumetric rendering of a relatively complexmodel of the normal glenoid vault morphology of the scapulae sample;

FIG. 9 shows views of a volumetric rendering of an intermediate 3-Dmodel of the normal glenoid vault morphology of the scapulae samplebased on the relatively complex 3-D model of FIG. 8;

FIG. 10 shows a perspective view of a simplified 3-D model of theaverage normal glenoid vault morphology of the scapulae sample based onthe intermediate 3-D model of FIG. 9;

FIG. 11 shows a superior view of each of the triangular cross sectionsof the simplified 3-D model of FIG. 10;

FIG. 12 shows a table listing the respective width dimension, depthdimension, and resulting area of the triangular cross sections of thesimplified 3-D model of FIG.10; and

FIG. 13 shows a table listing the coordinates for the respectivevertexes of the triangular cross sections of the simplified 3-D model ofFIG. 10 relative to the rectangular (“Cartesian”) coordinates referencesystem of FIG. 3.

DETAILED DESCRIPTION

Like reference numerals refer to like parts throughout the followingdescription and the accompanying drawings.

FIG. 1 shows an exploded perspective view of an exemplary shoulderprosthesis 100 including an exemplary glenoid component 120 according tothe present invention. Prosthesis 100 also includes an exemplary humeralcomponent 140. Humeral component 140 is configured in a known manner forimplantation in a humerus 160 and replacement of a natural humeral head(not shown) and, accordingly, includes a prosthetic humeral head 180.

Glenoid component 120 is configured for implantation in a scapula 200and replacement of a natural glenoid fossa (not shown in FIG. 1).Glenoid component 120 includes a bearing 220. Bearing 220 is made from adurable biocompatible plastic or any other suitable durablebiocompatible material. For example, bearing 220 may be made from apolyethylene. One particular polyethylene that is well suited forbearing 220 is a high molecular weight polyethylene, for exampleultra-high molecular weight polyethylene (“UHMWPE”). One such UHMWPE issold as by Johnson & Johnson of New Brunswick, N.J. as MARATHON™ UHMWPEand is more fully described in U.S. Pat. Nos. 6,228,900 and 6,281,264 toMcKellop, which are incorporated herein by reference. Bearing 220includes a generally concave surface 240 that is configured as known forbearing against prosthetic humeral head 180 or, in cases where thenatural humeral head is spared, for bearing against the natural humeralhead. Bearing 220 further includes a post 260, or some other feature ormechanism capable of mating the bearing to a stem element of the glenoidcomponent, such as stem 280 discussed below.

Glenoid component 120 also includes a stem 280. As discussed furtherbelow, stem 280 is configured to model a normal or pathologic glenoidvault morphology such that stem 280 fits within a cavity 300 that may bedefined, at least partially, by endosteal walls 320 of scapula 200. Tothis end, it is noted that the present invention may provide a series ofrigidly scaled or sized versions of stem 280 for accommodating variousglenoid vault sizes that may be presented among different patients. Itshould also be appreciated that the glenoid vault of scapula 200 mayinclude some cancellous bone 340.

Stem 280 is made from a suitable biocompatible metal such as, forexample, a cobalt chromium alloy, a stainless steel alloy, a titaniumalloy, or any other suitable durable material. In alternativeembodiments, stem 280 may include a porous coating to facilitate bonein-growth into glenoid component 120. The porous coating may be anysuitable porous coating and may for example be POROCOAT®, a product ofJohnson & Johnson of New Brunswick, N.J. and more fully described inU.S. Pat. No. 3,855,638 to Pilliar, which is incorporated herein byreference. Stem 280 can be solid or a thin shell of suitable durablematerial.

Stem 280 includes a generally superior surface 360, a generally inferiorsurface 380, a generally anterior-medial surface 400, a generallyposterior-medial surface 420, and a generally lateral surface 440. Stem280 defines a socket 460 that extends inwardly from surface 440. Socket460 receives post 260 (of bearing 220). Stem 280 may also define athrough-channel 480 that extends, coaxially with socket 460, throughstem 280.

Glenoid component 120 further includes a fastener 500 in the form of,for example, a screw. The screw, or screws, may be any screw capable ofadditionally securing glenoid component 120 within scapula 200. Forexample, the screw may be a cortical screw such as DePuy Ace catalognumber 8150-36-030 available from DePuy Orthopaedics, Inc. of Warsaw,Ind. The screw has a diameter sufficient to properly secure glenoidcomponent 120 within scapula 200 and may, for example, have a diameterof about two to five millimeters. The screw may have any suitable lengthcapable of properly securing glenoid component 120 within scapula 200.For example, the screw may have a length of from 10 to 60 millimeters.The screw may be secured to stem 280 in any suitable manner. In theexemplary embodiment, fastener 500 extends through through-channel 480(of stem 280). However, it is noted that fastener 500 is notindispensable and may be omitted from alternative embodiments.

Bearing 220 is secured to stem 280 in any suitable manner. For example,bearing 220 may be bonded to stem 280, or bearing 220 could be made frompolyethylene and compression molded to stem 280. Alternately, thebearing 220 may be glued to stem 280 by, for example, an adhesive.Alternatively, bearing 220 may be mechanically interlocked to stem 280by taper locking or otherwise press-fitting post 260 in socket 460, orpost 260 and socket 460 may include any other suitable interlockingfeatures, for example, rib(s), lip(s), detent(s), and/or otherprotrusion(s) and mating groove(s), channel(s), or indent(s) (notshown). Additionally, it is noted that in alternative embodiments,bearing 220 and stem 280 may be integrated into a single part made fromUHMWPE or any other suitable material—with or without an omission offastener 500.

The present invention contemplates a method for preparing a glenoidcomponent that will satisfy a majority of patient anatomies. Thus, inaccordance with one method, the steps described in flow diagrams ofFIGS. 2 a-2 c correspond to one exemplary method used to model thenormal or pathologic glenoid vault morphology, and ultimately to preparean optimally sized and configured implant.

In a first step 1020 (FIG. 2 a), a suitable sample of human scapulae(“scapulae sample”) is selected to represent a reasonable demographiccross section of an anticipated patient population. In the exemplaryembodiment, the scapulae sample included sixty-one human scapulaeselected from different sources, thirty-two left-sided and twenty-eightright-sided. Various criteria were applied to the selection process sothat the sample was as representative of the patient population aspossible, including height, sex, gender and ethnicity.

At step 1040 (FIG. 2 a), volumetric scan of each scapula in the samplewas performed using a Siemens Volume Zoom Scanner (a CT scanneravailable from Siemens Medical Systems of Malvern, Pa.). It is notedthat the initial orientation of the scapulae in the CT images isdependent on the physical placement and orientation of the scapulaewithin the CT scanner, which is inherently difficult to reproduce.Nevertheless, the scapulae were placed in a supine anatomic position andaxial images were obtained in one mm increments (with 0.27 to 0.35 mmin-plane resolution). The images were acquired at 120 kV, 100 mA, usinga 180 mm field-of-view, large focal spot, and rotation speed of 0.5sec/rev. A medium-smooth reconstruction algorithm was used forreconstruction of the images.

FIG. 3 shows a rectangular (“Cartesian”) coordinates reference system1060 relative to the plane body of a typical scapula 1080 as defined bythree surface points 1100, 1120, and 1140 of the scapula 1080. As atleast partially discernable from FIG. 3, point 1100 represents aninferior tip of the scapula 1080, point 1120 represents a medial pole ofthe scapula 1080 where the spine intersects the scapula 1080, and point1140 represents the center of the typical glenoid fossa 1160. Further,it should be appreciated that coordinates reference system 1060 defines,among other things, an XZ-plane 1180, an XY-plane 1190, a vector 1200extending from the medial pole of the scapula to the center of theglenoid fossa 1160, and an X-axis 1220.

At step 1230 (FIG. 2 a), the three-dimensional (“3-D”) images of thescapulae were re-sampled to align them on coordinates reference system1060 (see FIG. 3) for subsequent analysis. In the exemplary embodiment,points 1100, 1120, and 1140 were interactively chosen on the 3-D imageof each scapula and the scapulae were again re-sampled such that theplane of the body of each scapula was aligned parallel to the XZ-plane1180 of the coordinates reference system 1060 (see FIG. 3), and suchthat the vector 1200 extending from the medial pole of the scapula tothe center of the glenoid fossa 1160 was parallel to the X-axis 1220(see FIG. 3).

FIG. 4 shows the superior-inferior (“SI”) dimension 1240 and theanterior-posterior (“AP”) dimension 1260 of the glenoid fossa 1160. Atstep 1280 (FIG. 2 a), the SI dimension 1240 and the AP dimension 1260(see FIG. 4) of each scapula was determined by interactively placingpoints on the 3-D images using a suitable software program.

At step 1300 (FIG. 2 a), the scapulae sample were arbitrarily dividedinto six sub-groups based on their SI dimensions 1240 (see FIG. 4) toreduce the initial number of morphological comparisons and to facilitatedetermination of the relationship between the global or overall typicalglenoid vault size and the typical glenoid vault morphology. FIG. 5shows a table listing exemplary range and exemplary average SI dimensionfor the six sub-groups of scapulae based on their SI dimensions.

At step 1420 (FIG. 2 a), the endosteal walls 320 of the glenoid vaultsof the scapulae were manually traced and digitized. FIG. 6 shows asubstantially complete tracing 1320 (toward the inferior end of thetypical glenoid fossa 1160) of the endosteal walls 320 of the typicalglenoid fossa 1160. FIG. 7 shows a partial tracing 1360 (toward theinferior end of the typical glenoid fossa 1160) of the endosteal walls320 of the typical glenoid fossa 1160 as a result of fossa occlusion inthe region of the typical scapular spine 1380. Reference line 1400 (FIG.7) is discussed further below. Each endosteal boundary was traced oneach of the two-dimensional (“2-D”) XY-slices of the respectivere-sampled image (see FIG. 6), starting at the respective glenoid fossaand extending medially to the scapular spine 1380 (see FIG. 7), but notinto the interior of the spine. Both the anterior and posterior walltracings in the region of the spine are terminated at reference line1400 (see FIG. 7), which was defined to be simultaneously perpendicularto the plane of the respective glenoid fossa and tangential to thesurface of the respective endosteal notch.

At step 1440 (FIG. 2 a), each endosteal tracing defining the respectiveglenoid vault was normalized by its extent in the SI dimension. Thismeasurement was made from the inferior limit of the endosteal walls ofthe glenoid fossa to the superior limit in the Z-dimension (see FIG. 3)of the image. The vaults were rigidly scaled in all three dimensions(i.e., X, Y, and Z) to normalize the SI dimension of the vault tracingto the average within its corresponding sub-grouping. This approachsubstantially eliminated size differences between the different vaults,facilitating an appropriate shape determination. An assumption was madethat right-sided and left-sided scapulae are approximately anatomicallysymmetrical. Under this assumption, right-sided vaults were mirroredabout the XZ-plane (see FIG. 3) to allow morphological determinations tobe made within the entire sample. In the exemplary embodiment, thenormalized vaults within each of the six scapular sub-groupings werespatially aligned (i.e., “registered”) using an iterative closet point(“ICP”) algorithm such as discussed in Besl P. J. and McKay N. D., “Amethod for registration of 3-D shapes,” IEEE Trans. Pattern Analysis andMachine Intelligence 1992, volume 14, pages 239-256, which isincorporated herein by reference.

At step 1460 (FIG. 2 b), a 3-D model of the normalized glenoid vaultmorphology was then constructed for each sub-group of the scapulae ofthe scapulae sample based on the morphological constraints imposed byeach of the vaults in the sub-group. For each sub-group, the set ofregistered glenoid vaults were overlaid and the approximate averageendosteal walls 320 (see FIG. 6 and FIG. 7) of the sub-group weremanually digitized. Each endosteal boundary was traced on each of thetwo-dimensional (“2-D”) XY-slices of the respective re-sampled image(see FIG. 6), starting at the respective glenoid fossa and extendingmedially to the scapular spine 1380 (see FIG. 7), but not into theinterior of the spine. Both the anterior and posterior wall tracings inthe region of the spine were terminated at reference line 1400 (see FIG.7), which was defined to be simultaneously perpendicular to the plane ofthe respective glenoid fossa and tangential to the surface of therespective endosteal notch. The resulting 3-D model satisfied theendosteal wall boundaries for each vault within the group.

At step 1480 (FIG. 2 b), a relatively complex 3-D model 1500 (see FIG.8) approximating the average normalized glenoid vault morphology of theentire scapulae sample was constructed based on the morphologicalconstraints imposed by the models for each sub-group. The registeredglenoid vaults for the sub-groups were overlaid and the approximateaverage endosteal walls 320 (see FIG. 6 and FIG. 7) of the sub-groupmodels were manually digitized. Each endosteal boundary was again tracedon each of the two-dimensional (“2-D”) XY-slices of the respectivere-sampled image (see FIG. 6), starting at the respective glenoid fossaand extending medially to the scapular spine 1380 (see FIG. 7), but notinto the interior of the spine. Both the anterior and posterior walltracings in the region of the spine were terminated at reference line1400 (see FIG. 7), which was defined to be simultaneously perpendicularto the plane of the respective glenoid fossa and tangential to thesurface of the respective endosteal notch. The resulting 3-D model 1500satisfies the endosteal wall boundaries for each vault within thescapulae sample.

FIG. 8 shows views of a volumetric rendering of the relatively complex3-D model 1500 generated in the previous steps. As at least partiallydiscernable in FIG. 8, model 1500 includes a generally superior surface1520, a generally inferior surface 1540, a generally anterior-medialsurface 1560, a generally posterior-medial surface 1580, and a generallylateral surface 1600. It should be appreciated that generally superiorsurface 360 (of stem 280) corresponds roughly to generally superiorsurface 1520, generally inferior surface 380 (of stem 280) correspondsroughly to generally inferior surface 1540, generally anterior-medialsurface 400 (of stem 280) corresponds roughly to generallyanterior-medial surface 1560, generally posterior-medial surface 420 (ofstem 280)corresponds roughly to generally posterior-medial surface 1580,and generally lateral surface 440 (of stem 280) corresponds roughly togenerally lateral surface 1600.

At step 1720 (FIG. 2 b), intermediate 3-D model 1700 was constructed byinscribing a plurality of mutually parallel triangular cross sectionswithin the boundaries defined by the model walls on a plurality ofXY-plane (see FIG. 3) cross-sections of relatively complex 3-D model1500 (see FIG. 8). FIG. 9 shows views of a volumetric rendering of thisintermediate 3-D model 1700 of the normalized glenoid vault morphologyof the scapulae sample based on relatively complex 3-D model 1500 (seeFIG. 8).

At step 1800 (FIG. 2 b), a simplified 3-D model 1820 (see FIG. 10) ofthe average normalized glenoid vault morphology of the scapulae samplewas constructed by selecting five equidistantly inferior-superiorspaced-apart mutually parallel triangular cross sections (1840, 1860,1880, 1900, 1920) (see FIGS. 10 and 11) from intermediate 3-D model 1700(see FIG. 9). These triangular cross-sections were selected to accountfor more than 90% of the volume of intermediate 3-D model 1700 withalmost negligible spatial deviation of the anterior and posterior walls.It should be appreciated that simplified 3-D model 1820 thus provides aconcise geometrical model of the normalized glenoid vault morphologywhile substantially preserving the morphological nuances inherent to theendosteal walls 320 (see FIG. 1).

A perspective view of this simplified 3-D model 1820 of the averagenormalized glenoid vault morphology of the scapulae sample is shown inFIG. 10. FIG. 11 shows a superior view of each of the triangular crosssections (1840, 1860, 1880, 1900, 1920) obtained from the simplified 3-Dmodel 1820. As at least partially discernable from FIGS. 10 and 11,cross section 1840 includes a generally medially positioned vertex 2000,a generally anteriorly and generally laterally positioned vertex 2020,and a generally posteriorly and generally laterally positioned vertex2040. Similarly, cross section 1860 includes a generally mediallypositioned vertex 2060, a generally anteriorly and generally laterallypositioned vertex 2080, and a generally posteriorly and generallylaterally positioned vertex 2100. Cross section 1880 includes agenerally medially positioned vertex 2120, a generally anteriorly andgenerally laterally positioned vertex 2140, and a generally posteriorlyand generally laterally positioned vertex 2160. The next cross section1900 includes a generally medially positioned vertex 2180, a generallyanteriorly and generally laterally positioned vertex 2200, and agenerally posteriorly and generally laterally positioned vertex 2220.Finally, cross section 1920 includes a generally medially positionedvertex 2240, a generally anteriorly and generally laterally positionedvertex 2260, and a generally posteriorly and generally laterallypositioned vertex 2280.

Further, cross section 1840 includes a “base” edge 2400 extendingbetween vertex 2020 and vertex 2040, cross section 1860 includes a“base” edge 2420 extending between vertex 2080 and vertex 2100, crosssection 1880 includes a “base” edge 2440 extending between vertex 2140and vertex 2160, cross section 1900 includes a “base” edge 2460extending between vertex 2200 and vertex 2220, and cross section 1920includes a “base” edge 2680 extending between vertex 2240 and vertex2280.

In addition, cross section 1840 includes a “left” edge 2500 extendingbetween vertex 2000 and vertex 2020, cross section 1860 includes a“left” edge 2520 extending between vertex 2060 and vertex 2080, crosssection 1880 includes a “left” edge 2540 extending between vertex 2120and vertex 2140, cross section 1900 includes a “left” edge 2560extending between vertex 2180 and vertex 2200, and cross section 1920includes a “left” edge 2580 extending between vertex 2240 and vertex2260.

Finally, cross section 1840 includes a “right” edge 2600 extendingbetween vertex 2000 and vertex 2040, cross section 1860 includes a“right” edge 2620 extending between vertex 2060 and vertex 2100, crosssection 1880 includes a “right” edge 2640 extending between vertex 2120and vertex 2160, cross section 1900 includes a “right” edge 2660extending between vertex 2180 and vertex 2220, and cross section 1920includes a “right” edge 2480 extending between vertex 2260 and vertex2280.

The respective base edges (2400, 2420, 2440, 2460, 2680) of thetriangular cross sections (1840, 1860, 1880, 1900, 1920) define lateralboundaries of simplified 3-D model 1820, corresponding to the region ofthe typical glenoid fossa 1160 (see FIG. 3). Further, the respectiveleft edges (2500, 2520, 2540, 2560, 2580) of triangular cross sections(1840, 1860, 1880, 1900, 1920) define anterior boundaries of simplified3-D model 1820, while the respective “right” edges (2600, 2620, 2640,2660, 2480) of triangular cross sections (1840, 1860, 1880, 1900, 1920)define posterior boundaries of simplified 3-D model 1820. The respectivegenerally medially positioned vertexes (2000, 2060, 2120, 2180, 2260) oftriangular cross sections (1840, 1860, 1880, 1900, 1920) sweep from amore posterior orientation at the inferior end of simplified 3-D model1820 to a more anterior orientation at the superior end of simplified3-D model 1820.

Each of the triangular cross sections (1840, 1860, 1880, 1900, 1920) hasa respective width dimension (“w”) and a depth dimension (“d”). Thetable in FIG. 12 summarizes the respective width dimension (“w”) (seeFIG. 11), depth dimension (“d”) (see FIG. 11), and resulting area oftriangular cross sections (1840, 1860, 1880, 1900, 1920). The table inFIG. 13 lists the coordinates for the respective vertexes of triangularcross sections (1840, 1860, 1880, 1900, 1920) relative to rectangular(“Cartesian”) coordinates reference system 1060 (see FIG. 3).

It is contemplated that simplified 3-D model 1820 may be rigidly scaledaccording to SI size (see FIG. 4) to accommodate larger or smallerglenoid vaults while maintaining the integrity of the basicmorphological model.

At step 3000 (FIG. 2 c), stem 280 is initially fashioned in the shape ofthe simplified 3-D model 1820. In one embodiment, this step 3000contemplates loading the coordinates of each of the vertexes definingthe simplified 3-D geometrical model 1820 into a suitable stereolithography system. The stereo lithography system may be operated toproduce a corresponding 3-D form made of a plastic, wax, or any othersuitable material as is known in the art. A mold is then prepared fromthe 3-D form and a stem 280 is fashioned, such as by injection moldingusing this mold. In alternative embodiments stem 280 may be otherwisesuitably produced in accordance with simplified 3-D model 1820 viastereo lithography, by hand, or by any other suitable method (with orwithout an intervening form or mold) as known.

In subsequent steps, the stem 280 is machined to provide the featuresnecessary to prepare the stem for implantation. Thus, at step 3020 (FIG.2 c), socket 460 is bored into stem 280. At step 3040 (FIG. 2 c),through-channel 480 is bored (coaxially with socket 460) through stem280. It should be understood that the rough stem produced from the 3-Dmodel may be machined according to other protocols depending upon theinterface between the stem 280 and the bearing 220. It is furthercontemplated that the stem 280 may be formed as a solid or a hollow bodyand may further be provided with certain surface features to facilitatefixation of the stem within the glenoid vault.

The improved stem may then be implanted in accordance with knownsurgical procedures. For instance, cancellous bone 340 may first beremoved from the glenoid vault of scapula 200 to construct cavity 300,which extends to endosteal walls 320 (see FIG. 1). Stem 280 is theninserted into cavity 300 into intimate contact with endosteal walls 320to facilitate alignment and reliable fixation of glenoid component 120within scapula 200. Bone cement may be used to enhance fixation of thestem within the bone. Fastener 480 is inserted through through-channel480 into engagement with scapula 200. After fastener 480 is fullyinserted into scapula 200, post 260 is inserted into socket 460 andbearing 220 is secured to stem 280.

The foregoing description of the invention is illustrative only, and isnot intended to limit the scope of the invention to the precise termsset forth. Further, although the invention has been described in detailwith reference to certain illustrative embodiments, variations andmodifications exist within the scope and spirit of the invention asdescribed and defined in the following claims.

For example, the glenoid components may be solid or hollow bodies. Inparticular, the stem 280 may be formed as a solid implant, but may bepreferably at least partially hollow to reduce the weight and materialrequirements for the component. If the implant component is hollow, itmust have sufficient wall thickness to maintain its strength andintegrity under maximum expected physiological loads.

The present invention contemplates a glenoid stem component that isformed to closely approximate a normalized glenoid vault morphology. Inthe embodiments discussed above, this normalized morphology is generatedfrom a relatively large sample size of human scapulae from whichrelevant measurements were obtained. It was found that the normalizedcomponent dimensions obtained in accordance with the invention wellapproximated the actual dimensions of the sample population. Inparticular, it was found that at least 85% of the surface points of thesampled glenoid vaults varied by less than 2.0 mm, which represents aminimal variation given the overall dimensions of the endosteal walls ofthe vault.

In generating the vault models for the different groups noted above, itwas discovered that for the entire set of vault geometries, 98.5% of thesurface points comprising the interior surface models varied by lessthan 2.0 mm. This finding refuted the a prior assumption that vaultmorphology was dependent upon the global vault size. As a result, asingle vault model was derived from the group models using the samesteps described above. This final model is depicted in FIG. 9. From thatmodel of the actual glenoid vault morphology for the entire samplepopulation, the simplified geometric model was developed as describedabove. This simplified model was found to account for over 80% of thevolume of the model of the actual sample population, while alsopreserving the morphological nuances inherent to the endosteal surfacesof the glenoid vault.

In one aspect of the invention, a morphological model is developed forseveral discrete groups of glenoid sizes. The groups may be preferablygrouped by SI (superior-inferior) dimension, as summarized in the tableof FIG. 5. The simplified model used to create the component mold in theillustrated embodiment corresponded to Group 4, but it is understoodthat the simplified model for the other groups may be obtained bydirectly scaling the dimensions as a function of the ratio of SI values.

1. A glenoid component apparatus for shoulder arthroplasty, theapparatus comprising: a bearing portion configured to engage a bearingelement associated with the humerus; and a stem portion connected tosaid bearing portion; wherein said stem portion models a normalizedglenoid vault morphology, wherein said stem portion includes a pluralityof mutually substantially parallel triangular cross sections that arespaced apart along a dimension of said stem portion, and wherein saidplurality of mutually parallel triangular cross sections includes: afirst triangular cross section having a width and having a depth about2.8 times the width; a second triangular cross section having a widthabout 2.2 times the width of the first triangular cross section andhaving a depth about 2 times the width of the first triangular crosssection; a third triangular cross section having a width about 2.2 timesthe width of the first triangular cross section and having a depth about1.8 times the width of the first triangular cross section; a fourthtriangular cross section having a width about 1.7 times the width of thefirst triangular cross section and having a depth about 2 times thewidth of the first triangular cross section; and a fifth triangularcross section having a width about equal to the width of the firsttriangular cross section and having a depth about 2.2 times the width ofthe first triangular cross section.
 2. The apparatus of claim 1,wherein: the first triangular cross section includes a vertex relativelypositioned at Cartesian coordinates (X,Y,Z) of about (28, 8, 0), thefirst triangular cross section includes a vertex relatively positionedat Cartesian coordinates (X,Y,Z) of about (0, 15, 0), the firsttriangular cross section includes a vertex relatively positioned atCartesian coordinates (X,Y,Z) of about (28, 18, 0), the secondtriangular cross section includes a vertex relatively positioned atCartesian coordinates (X,Y,Z) of about (29, 1, 8), the second triangularcross section includes a vertex relatively positioned at Cartesiancoordinates (X,Y,Z) of about (9, 14, 8), the second triangular crosssection includes a vertex relatively positioned at Cartesian coordinates(X,Y,Z) of about (28, 23, 8), the third triangular cross sectionincludes a vertex relatively positioned at Cartesian coordinates (X,Y,Z)of about (29, 0.5, 16), the third triangular cross section includes avertex relatively positioned at Cartesian coordinates (X,Y,Z) of about(10.5, 11, 16), the third triangular cross section includes a vertexrelatively positioned at Cartesian coordinates (X,Y,Z) of about (28, 23,16), the fourth triangular cross section includes a vertex relativelypositioned at Cartesian coordinates (X,Y,Z) of about (29, 2.5, 24), thefourth triangular cross section includes a vertex relatively positionedat Cartesian coordinates (X,Y,Z) of about (8, 7, 24), the fourthtriangular cross section includes a vertex relatively positioned atCartesian coordinates (X,Y,Z) of about (28, 20, 24), the fifthtriangular cross section includes a vertex relatively positioned atCartesian coordinates (X,Y,Z) of about (29, 3.5, 32.5), the fifthtriangular cross section includes a vertex relatively positioned atCartesian coordinates (X,Y,Z) of about (6, 0, 32.5), and the fifthtriangular cross section includes a vertex relatively positioned atCartesian coordinates (X,Y,Z) of about (28.5, 14, 32.5).